1. Field of the Invention
The present invention relates to a process for displaying information, especially on a flat panel display.
2. Description of the Prior Art
The present display technology is evolving rapidly towards flat panel structures replacing the bulky and power consuming CRT in a number of applications where high resolution is not a primary concern.
This new generation of displays covers two main categories, namely the active and passive displays.
Active displays generate light on a flat surface, according to the visual pattern to be displayed. They are very much like the screen of a CRT and present the advantages and restrictions of the latter. For example, the visibility depends on the light environment and a bright light falling on the screen hampers its readability.
Passive displays reflect or absorb light selectively to form the pattern building up the image. They are similar to a printed sheet of paper: the higher the ambient light is, the better the picture. They are most suitable for operation in high ambient light conditions.
The addressing of a flat display is generally based on digital control over a crossbar conductor system where picture elements are located at orthogonal X-Y intersections. TV-type scanning is possible using shift registers for addressing the X-Y intersections row-by-row in raster fashion.
A number of flat displays have been suggested in the past decade, and the various types are distributed between the passive (light modulating) types such as:
Liquid Crystals Displays (LCD) PA1 Magneto Optics Displays (MOD) PA1 Electrochromic Displays (ECD) PA1 Light emitting diodes arrays (LED) PA1 Plasma panels (GDD) PA1 Electroluminescent displays (ELD)
and the active (light generating) types such as:
Liquid crystal displays (LCD) are by far the most successful flat display on the market today. They are relatively economical to build, provide a fair contrast image with a resolution which is now comparable to the cathode ray tube, they can also provide a color image with somewhat lower resolution than monochrome. However, they have the drawback of providing a variable contrast with the angle of vision of the image. The addressing time is still relatively slow and they need complicated circuitry for TV scanning.
Magneto optics displays (MOD) are still very expensive to produce due to the fact that they require monocrystals which are necessarily expensive (large crystals) or need an assembly of smaller crystals in a mosaic structure. Magneto Optics Displays are also difficult to address and require higher signal voltages than the liquid crystal display.
Electrochromic displays (ECD) are the next best choice for a flat display after liquid crystals. They have the advantage over the liquid crystal display in providing an optical density based on the absorption of light rather than on scattering, which eliminates the variation of contrast with the direction of viewing. They are simpler in structure than the liquid crystal display and would probably lead to more economical manufacturing. The drawback at present is their slow response time and short life.
In the category of active displays, which present the inconvenience of restricted viewing in high light environments, the light emitting diode array (LED) is an expensive display both from the point of view of manufacturing cost and power consumption; also, the resolution is limited by the smallest size of the individual diodes. Color display is possible but with much lower resolution than the passive liquid crystal display.
Plasma panels (GDD) have proven to be competitive with the LED arrays at a much lower price. The main drawbacks are low resolution and limited lifetime.
The electroluminescent display (ELD), especially the thin film ELD, is probably the only active display which can compete with the passive liquid crystal display. This type of display has a higher resolution and is economical to manufacture. However, color display still presents a problem, as does lifetime.